Invalid mailbox syntax is used Error
You can find Invalid mailbox syntax is used error under the To, From, Subject or Additional Headers fields, that are located in the Mail Contact Form tab.
solve “Your contact form has a configuration issue” error
You have to solve this error. Otherwise, your email might not reach the addressee.
To cope with this error you might need to accomplish the next steps.
1] First, add valid email address to the To field (e. g., [email protected]).
2] Make sure that you use correct syntax in the From field (e. g., [your name] <[your-email]>).
3] Fill in your email subject to add information on your email (e.g., Site Name – [your-subject]).
4] You can add new fields to your contact form (e.g. phone number, city, etc.). Add the necessary content in the Additional Headers block (for instance, Phone: [phone]).
“This field can be empty depending on user input” Error
You can face This field can be empty depending on user input error if you’ve left Additional Headers or Subject fields empty.
If you don’t want to use these fields, you may leave them empty, as they won’t influence sending messages.
But if you face this error in To, From or Message fields, you’ll have Failed to send your message error when submitting a contact form.
Fill in the fields correctly to avoid these kinds of errors.